The present invention relates to aircraft engine inlets, and more particularly, to variable area inlets for supersonic and subsonic aircraft.
A supersonic inlet is a sub-component of an aircraft propulsion system for high speed supersonic aircraft. The supersonic inlet should be designed to efficiently decelerate the approaching high speed airflow to speeds that are compatible with efficient turbojet engine operation and to provide optimum matching of inlet and engine airflow requirements. Entrance airflow speeds to existing airbreathing engines must be subsonic; therefore, it is necessary to decelerate the airflow speed during supersonic flight. Typically, engine entrance Mach numbers for supersonic propulsion systems are 0.3 to 0.4. The inlet must reduce the velocity of the approaching airflow to these subsonic levels while maintaining a minimum of loss in freestream total pressure and while maintaining a near uniform flow profile at the engine entrance. In addition, it is essential that the inlet diffuse the air in a manner to minimize the pressure losses, cowl and additive drag, and flow distortion.
Prior art mixed compression inlets designed for supersonic cruise conditions have not been able to achieve high performance, reduced weight and mechanical complexity, as well as supply the large amount of engine airflow required for transonic conditions and takeoff conditions. The inlet must also have a wide range of operability where safety is an important consideration in order to ensure that the inlet will absorb airflow disturbances that can trigger an inlet unstart, which is a potentially dangerous condition which occurs when the normal shock moves out of the inlet duct to a position upstream of the cowl lip, and results in a rapid decrease in flight speed and engine power. Thus prior art inlets have generally traded off one or more important performance parameters at the expense of another. For example, the traditional xe2x80x9ctranslating centerbodyxe2x80x9d (TCB) axisymmetric inlet has a narrow operability margin and is limited in its transonic airflow capability. Another type of mixed compression inlet known as the xe2x80x9cvariable diameter axisymmetric centerbodyxe2x80x9d (VDC) inlet is very mechanically complex and may result in high maintenance or manufacturing costs. A third type of mixed compression inlet referred to as a xe2x80x9ctwo-dimensionalxe2x80x9d (2D) inlet is heavy and may impose an integration drag penalty when compared to the axisymmetric designs.
Thus it is desired to have a new and improved inlet design which provides the high performance, required transonic airflow, while maintaining an acceptable operability margin for external disturbances.
The present invention provides an inlet with a new variable geometry scheme that enables a breakthrough in axisymmetric inlet design and offers a large transonic flow capability while maintaining adequate operability margin and high performance at cruise conditions.
The invention provides in one aspect an inlet for use in an aircraft comprising an axisymetric centerbody comprising an inner annular wall and a curved exterior surface of varying height along a longitudinal axis of the centerbody. A cowl partially encloses the centerbody and forms a duct therebetween. The centerbody further includes one or more slots, with each slot having an end wall extending radially upward from the inner annular wall of the centerbody and an upper wall extending from the end wall forming an interior cavity within the slot. The centerbody additionally includes one or more segments slidably mounted upon the inner wall of the centerbody and positioned for reception into the interior cavity of an adjacent slot, wherein a longitudinal channel is formed when the segment is slidably positioned within the slot.
The invention provides in another aspect an inlet for use in an aircraft comprising a translating axisymetric centerbody having a curved exterior surface of varying height along a longitudinal axis of the centerbody, and a cowl mounted about the centerbody and forming an annular duct therein. The centerbody further includes one or more channels formed on the periphery of the centerbody, with each channel having opposed sidewalls extending longitudinally along the centerbody and a bottom wall connecting the sidewalls. The centerbody further includes one or more slidable segments for insertion into a respective channel, each of the segments having a first portion having a first end hinged to a stationary section of the inlet and a second portion rotatably connected to the first portion and slidably mounted within opposed grooves of the channel sidewall so that when the inlet centerbody translates foreward the segments slide within the grooves exposing the channels.
The invention provides in yet another aspect an inlet for use in an aircraft comprising an axisymetric centerbody having a curved exterior surface of varying height along a longitudinal axis of the centerbody and a cowl mounted about the centerbody and forming an annular duct therein. The centerbody further includes one or more channels formed on the periphery of the centerbody, with each channel having opposed sidewalls extending longitudinally along the centerbody and a bottom wall connecting the sidewalls. The centerbody further includes one or more slidable segments for insertion into a respective channel, each of the segments having a first portion having a first end hinged to a stationary section of the inlet, and a second portion rotatably connected to the first portion and slidably mounted within opposed grooves of the channel sidewall so that the channel is exposed when the segments slide within the grooves.